You can expect to be very sore, lol... Just do your best, don't go heavy, and absorb all the info you are given. Don't be mad at yourself if you have to scale. You might be surprised how short the workout is, depending on what other kinds of workouts you've tried in the past. Some of them are only 20 minutes! That is one of the many reasons I love CrossFit. You will get a better workout in those 20 minutes than most people get in an hour of random machines and ellipticals at the gym.